Granulating apparatus

ABSTRACT

A fine crystalline material is fed to a pressure screw rotating in a casing and conveying the material under pressure to the outlet of the casing. The material is pressed through an extruder head rotating directly in front of the outlet and provided with a plurality of perforations which are bounded at one side with a projecting nose which cuts a predetermined quantity out of the pressure supplied material to issue in form of granules. Separate drives are provided for adjusting the rotations per minute of the pressure screw and the extruder head separately.

United States Patent Moser et al. [4 1 Aug. 1, 1972 [54] GRANULATING APPARATUS [56] References Cited Inventor-s1 gi helm, M%e 1l7i 20%;? 12:? UNITED STATES PATENTS onnln en; e Heinz ickermann both 8 Bad 2,239,952 4/1941 Dergance ..241/92 X nonningen an of dermany 3,164,330 1/ 1965 Neidl ..241/ 186 A 3,193,601 7/1965 Billingsley ..18/12 SH [73] Assignee: Kali-Chemie Aktiengesellschaft, 3,502,125 3/ 1970 Desnick ..241/92 X Hannover, Germany Primary Examiner-R0bert L. Spruill [22] July 1970 Attorney-Michael S. Striker [21] Appl. No.: 53,956

. [57] ABSTRACT [30] Foreign Application Priority Data A fine crystalline material is fed to a pressure screw rotating in a casing and conveying the material under July 19, 1969 Germany ..P 19 36 923.4 pressure to the outlet of the casing. The material is I pressed through an extruder head rotating directly in 52 U.S. c1. ..241/93, 146/185, 241/280 from of the Outlet and pmlided with a Plurality 51 111:. CI ..B02c 18/30, B020 19/20, B02c 25/00 bwnded F [58] Field of Search ..241/85, 91, 92, 93, 186 A, Jeclmg mse a Predemmed quanmy 241/246, 247, 277, 280; 146/115, 123, 126, 175, 177,185; 18/12 SH, 12 SN of the pressure supplied material to issue in form of granules. Separate drives are provided for adjusting the rotations per minute of the pressure screw and the extruder head separately.

9 Claim, 6 Drawing Figures PATENTEDM 1 I972 3.680.798

sum 1 [1F 3 FIG. I

INVEYTORS 1 V: uau Masm BY V -MELA WlKKS AQb Hem/Z AckEWMi Ml.

PATENTEDMIB 1 I912 sum 2 OF 3 FIG. 2

FIG. 3

FIG. 4

INVENTORS'. J'wem a i P BY VILHELM L/uQKs KAm-HawAcuqMm/u M d :f.

diam-QM INVENTORS:

Mann. AQSER BACKGROUND OF THE INVENTION The present invention relates generally to the formation of granulates, and more particularly to an apparatus for forming granulates, particularly from substances having fine-crystalline shape.

There are many substances having fine-crystalline shape, for instance micro-crystalline shape, which are intended to be converted to granular form. one such substance is, by way of example, sodium perborate which will be discussed later in more detail. Because of the ready solubility of substances in this state they cannot be admixed with sufficient liquid-usually water-to be subjected to granulation in the customary well-accepted manner. On the other hand, the smallness of the crystals of such substances assures that in dry state the latter are bulky and have large volume; this, in turn, requires the admission andadmixture of substantial quantities of liquid before the crystals are sufficiently wetted and liquid coated to form a paste which can be readily worked and converted to granular state. Thus, substances of this type pose contrary requirements, namely on the one hand the need for the admission of substantial quantities of liquid and on the other hand the need to admit only relatively small quantities of liquid which is dictated by the ready solubility of these substances. The result is, of course, that the second need supercedes the first one so that only relatively small quantities of liquid are admitted to such substances with the concomitant difficulty that not all of the crystals are equally. liquid-coated so that a ready displacement of the crystals relative to one anotherand formation of a paste or dough which can be appropriately converted to granulated stateis impossible.

The outcome of these contrary requirements thus far has been that fine-crystalline substances of the type here under discussion have never been satisfactorily granulated in known granulating apparatus, such as granulating plates or screen-type devices through which the paste is pressed for granulating purposes. The impossibility to admit adequate quantities of liquid to the substances either prevents the formation of granules or permits the development of granules only whose coherence is so tenuous that during further processing they will again come apart to crystalline shape.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome the aforementioned difficulties.

More particularly it is an object of the present invention to provide a novel apparatus for simply and reliably granulating substances of fine-crystalline form.

In pursuance of the above object, and others which will become apparent hereafter, one feature of the invention resides in an apparatus for granulating a finecrystalline material which imparts to such a material a moisture content which should not exceed 30 percent and which may be under percent depending on the material to be granulated.

The moistened material is advanced under pressure in a barrel to an outlet of the latter via a pressure screw rotating in the barrel. As the material issues from the outlet it is subjected to granulation by the fact that directly proximal to the outlet there rotates an extruder head, this extruder head having a circumferential wall provided with a plurality of perforations through which the material is extruded to thereby become granulated.

The invention is based on the surprising realization that it is possible to properly extrude fine-crystalline substances or materials which cannot be adequately wetted, if they are subjected to requisite pressure before undergoing granulation. This compacts the crystals, reducing the interstices between them sufficiently so that the amount of moistening which can safely be tolerated in such materials is adequate to sufficiently coat the individual crystals and thus assure proper granulation.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and. advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic partly sectioned side-elevational view of an apparatus according to the present invention;

FIG. 2 is a somewhat diagrammatic axial section, on an enlarged scale, through a component of the apparatus illustrated in FIG. 1; 7

FIG. 3 is a fragmentary developed view of a portion of the cylindrical peripheral wall of the component shown in FIG. 2;

. FIG. 4 is a fragmentary sectional detail view, on an enlarged scale, illustrating a detail of the component in FIGS. 2 and 3;

FIG. 5 is a diagrammatic sectional elevation illustrating a further embodiment of the invention; and

FIG. 6 is a view similar toFIG. 5 but showing still another embodiment of the invention DESCRIPTION OF THE PREFERRED EMBODIMENTS the barrel 3 of a feed screw conveyor so that material from the hopper l enters the barrel 3 to be conveyed therein under pressure by a pressure screw 3b towards the remote outlet 3a of the barrel 3. The axes of rotation of the screws 2 and 3b extend normal to one another. Reference numeral 5 identifies diagrammatically a drive for the feed screw 2, whereas reference numeral 6 identities in similarly diagrammatic form a drive for the pressure screw 3b. Reference numeral 6a identifies a drive shaft and coupling connecting the feed screw 3b with its drive 6. A similar arrangement may of course be provided between the drive 5 and the screw 2. The drives 5 and 6 have not been illustrated in more detail because they may be of any conventional type utilized for driving the screws of the type here discussed, and do not form a part of the present invention. However, it is emphasized that the drives 5 and 6 permit independent adjustment of the rotations per minute of the screws 2 and 3b respectively.

The material entering the barrel 3 is advanced therein under pressure, being compacted in so advancing whereby the crystals are moved closer together with a reduction of the interstices between them, towards the outlet 3a of the barrel 3. According to the invention there is provided an extruder head 4 which rotates directly adjacent the outlet 3a about an axis which is normal to the axis of rotation of the screw 3b, for which purpose another separate diagrammatically illustrated drive 7 is provided. This drive 7 permits adjustment of the rotations per minute of the extruder head 4 independently of the rotations of the screws 2 and 3b.

The construction and arrangement of the screws 2 and 3b is such that the screw 2 feeds no more material through the outlet la into the barrel 3, than the screw 3b is capable of receiving and advancing per similar time unit. It will be noted that the screw 2 comprises a ribbon or band-shaped upper portion which is conically convoluted and therefore capable of yielding; the purpose of this is to accommodate possible deviations in the throughput of material through the outlet la so that if necessary material is capable of yielding in upward direction in the event that it cannot be accepted fast enough by the screw 3b. The latter, of course, is the one which exerts the pressure upon the material, with the pressure being greater as the number of rotations per minute of the screw 3b is increased.

Wetting of the material may be accomplished prior to or at the same time with its introduction into the hopper l. The compression to which the material is subjected in the barrel 3 assures that the relatively small percentage of moisture which may be added to the material without deleterious effect upon the same, is sufficient to permit proper granulation.

The granulation itself takes place as the material is extruded under pressure through apertures provided in the extruder head 4. Details of the extruder head are illustrated in FIGS. 2-4. It will be seen that it comprises a peripheral outer wall 8 in cylindrical form which consists of sheet material, such as sheet metal or the like, and which is provided with a plurality of apertures 11 (one illustrated in FIG. 4) through which the material is forced under pressure. Inside the hollow cylinder which is surrounded and defined by the peripheral wall 8 is a supporting structure 9 of suitable type, for instance that illustrated. TI-Ie purpose of the supporting structure 9 is to prevent collapse of the peripheral wall 8 and at the same time to permit mounting of the extruder head for rotation about its axis as illustrated in FIG. 1.

As FIG. 4 shows particularly clearly, the apertures in the wall 8 are providedor rather boundedat one side with a projecting nose 10 which cuts a predetermined quantity of the pressure-supplied material out of the supplied quantity, so that this predetermined quantity can pass through the aperture 1 1. FIG. 4 also shows that these noses or projections 10 are so configurated analogously to a hollow chisel, that is they are so configurated that their action when the extruder head 4 rotates resembles the action of a hollow chisel. Of

course, they are located at the outer side of the peripheral wall 8. The effectiveness of the extruder head 4 is improved further if the apertures are levelled at the side opposite the projections 10, as indicated at 10a in FIG. 4, so that the cutting-out of the predetermined quantity from the pressure-supplied material can take place readily and without any change in the crosssection of the material. The hollow-ground bevelling of the projections or noses 10 is advantageously accomplished at the same time as the bevelling 10a.

The apertures 11 of the wall 8 are arranged, as shown in FIG. 3, in mutually inclined rows, of which those extending in one direction define with the axis of the cylindrical head angles of 300 whereas the remaining ones define with the axial endface of the head 4 angles of 15. The diameter of each individual aperture may be on the order of approximately one to 1.5 mm. An arrangement have angles beta of 30 and alpha 10 gives also good results.

The material supplied under pressure by the screw 3b of course is pressed against the wall 8 under pressure, so that friction and consequent heating cannot be precluded. If the material is of the type which melts at low temperature, this would cause a smearing and closing of the apertures 11. This disadvantageous heating is completely avoided if the rotations per minute of the extruder head 4 are matched with the quantity of material issuing from the outlet 30 of the barrel 3, and the number of apertures 11 provided in the extruder head 4 and their size must of course be similarly matched to this purpose. In other words, there must be a quantitative removal of the material by the extruder head 4 which is extruded out of the outlet 3a of the barrel 3, because if insufficient material is extruded at the outlet 3, no pressure develops and no granulate will be formed, whereas on the other hand the excessive extrusion of material produces an excessive pressure and a consequent development of frictional heating and smearing, and closing of the apertures 1 1.

Another embodiment of the invention is shown in FIG. 4. In this granulating apparatus the extruder head has the form of a cone instead of a cylinder. The conical form of the extruder head has the advantage that the quantity of material which is cut out and granulated per minute is greater. This granulating apparatus consists of a cylindrical tube 15 in which the pressure screw 14 rotates advancing the material to be granulated under pressure to the conical extruder head 16a. The screw 14 is driven by the motor 12 via the shaft 13. The rotations per minute may be adjusted continuously. The granulation takes place in the extruder head 16a rotating directly proximal to the outlet of the cylindrical tube with the basis of the cone directly under the pressure screw and provided with a plurality of perforations, said perforations each being bounded in part by a wall portion projecting from the inner surface of the extruder head wall at one side of the respective perforations. The conical extruder head is driven by a continuously adjustable drive via shaft 18. Identified by reference numeral 17 is a channel to receive the granulates material.

In FIG. 6 a modified form of this construction is shown. It is distinguished from the construction shown in FIG. 5 by reversal of the conical extruder head, the vertex of the cone being directly under the pressure screw. In the granulating apparatus shown in FIG. 6 the material to be granulated is conveyed to the extruder head as described in the foregoing paragraph. The granulation takes place in the conical extruder head 16b, rotating directly proximal to the outlet of the cylindrical tube with the vertex of the cone directly under the pressure screw and provided with a plurality of perforations, said perforations each being bounded in part by a wall portion projecting from the outer surface of the extruder head wall at one side of the respective perforations. Identical parts of the granulating apparatus shown in FIG. 5 and in FIG. 6 are designated with the same reference numeral.

The present invention, that is the method and apparatus, is particularly advantageous but not limited in any sense with respect to the formation of granulates of sodium perborate. TI-lis material is very difficult to form into granules because it is highly watersoluble and has a low melting point, particularly if it is supplied in microcrystalline form as is its common configuration. The admission of water must be limited to between 15 and 25 percent because perborate begins to dissolve at a moisture content of approximately 30 percent. The result is that a crumbly rather dry raw material has heretofore had to be subjected to granulation, and accordingly the granulation attempts have not been successful until now.

The utilization of the present invention for granulating micro-crystalline sodium perborate will be described now by way of the following.

EXAMPLE 37 kg of micro-crystalline sodium perborate tetrahydrate with a moisture content of 19.6 percent was introduced into the hopper 1 of an apparatus according to the present invention as shown in FIG. 1. The rotations per minute of the screw 2 and 3b were set so that each screw performed approximately 20 rotations per minute; the rotations per minute of the extruder head 4 were regulated to approximately 120 rpm. The outlet opening 3a of the barrel 3 had a diameter of 100 mm, and the diameter of the extruder head 4 was 180 mm whereas its height was 140 mm. The extruder head, however, was provided only over a height of 1 mm in its wall 8 with the apertures 11. The total number of apertures was approximately 2900 which were arranged at angles of 30 and as shown in FIG. 3, with the diameter of each individual aperture 11 being 1.3 mm. It was found that this arrangement of the apertures was so far the most advantageous as smearing and closing of the apertures was avoided.

The granulate becomes available at the inner side of the wall 8 and, after drying in a fluidized bed in conventional manner, 26.5 kg of granulate was obtained with a diameter up to 1.3 mm per granule and a median diameter of approximately 0.5 mm. The granules were resistant to abrasion and were found not to fall apart into their constituent crystals during subsequent processing. They have an active oxygen content of approximately 10.4 percent, meaning that no significant loss of oxygen took place.

It will be appreciated, of course, that different diameters for the apertures 11 may be selected advantageously within a range of approximately one to 1.5 mm. If the apertures are larger than the 1.3 mm example mentioned above, then the angle at which the apertures are arranged must be steeper. Generally speaking, the number of rpm of the screws 2 and 3b may advantageously range between approximately 15-25 rotations per minute, but preferably is between 20 and 22 rpm. The speed of rotation of the extruder head 4 may be between and 150 rpm, preferably between 100 and 130 rpm. Speaking in general, the number of apertures 11 per square centimeter of area of the wall 8 may be between two and six, preferably on the order of four. The angles included between such apertures are 30 and 15, or 30 and 10.

The example set forth above was repeated under different conditions, in that the rpm of the pressure screw 3b and that of the extruder head 4 were varied, with the number, arrangement and size of the apertures 11 being changed. The appended table indicates what influence the change of a parameter exerted upon the characteristics of the granulate obtained.

TABLE ,No. of Apertures 2,900 1,800 2,900

Aperture Size 1.3 mm 1.3 mm 1.2 mm Aperture Arrangement Angle 30/15 30/15 30/15 RPM of Extruder Head RPM" 120 RPM 120 RPM RPM of Press Screw 21 RPM 21 RPM 21 RPM Hourly Throughput 50 kg/h 36 kg/h 42 kg/h Median Grain Size 0.40 mm 0.45 mm 0.45 mm Bulk Density 0.47 kg/] 0.49 kg/l 0.50 kg/l Abrasion l2 l0 9 No of Apertures 2,900 2,900 2,900 Aperture Size 1.3 mm 1.3 mm 1.3 mm Aperture Arrangement Angle 30/10 30/15 30/10 RPM of Extruder Head 120 RPM 100 RPM 120 RPM RPM of press Screw 21 RPM 21 RPM 17 RPM Hourly Throughput 46 kg/h 42 kg/h 40 kg/h Median Grain Size 0.37 mm 0.43 mm 0.35 mm Bulk Density 0.47 kg/l' 0.48 kg/l 0.46 kg/] Abrasion l3 10 13 If this RPM is exceeded, material being processed is in danger of melt- Granulaties being coarser because of the higher extrusion pressure. "With closer aperture spacing in direction of rotation, extrusion pressure decreases; this corresponds to a reduction in the bulk density. However, this is compensated by the increased bulk density of the necessarily finer granulate.

It will be under stood that each of the elements described above, or two or more together, may also find a useful application in other types of applications differing from the types described above.

While the invention has been illustrated and described as embodied in a granulating apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended l. A granulating apparatus comprising pressure-exerting conveying means including a casing having an outlet and a pressure screw rotating in said casing and operative for conveying material to be granulated towards said outlet under pressure; an extruder head rotating directly proximal to said outlet and being provided with a plurality of perforations, said perforations each being bounded in part by a wall portion projecting from a surface of the extruder head wall at one side of the respective perforations; and drive means for rotating said screw and said extruder head and for independently adjusting their respective speeds of rotation.

2. A granulating apparatus as defined in claim 1, further comprising supply means for material to be granulated, including a hopper having an exit and a feed screw rotatable about a first axis in said hopper for conveying material through said exit, said casing communicating with said exit for receiving said material therefrom and said pressure-screw rotating in said casing about a second axis inclined to said first axis; and wherein said extruder head rotates about a third axis normal to said second axis and has a cylindrical peripheral wall provided with said perforations through which said material is extruded for granulation.

3. An apparatus as defined in claim 2, said extruder head further comprising an internal support, and an intemal and reinforcing structure connected with said cylindrical wall.

4. An apparatus as defined in claim 2, wherein said perforations have diameters of between substantially one and 1.5 mm.

5. An apparatus as defined in claim 2, wherein said wall comprises between two and six apertures in each square centimeter of surface area, the apertures being arranged in first rows which define with the axis of rotation of said head angles of 30 and in second rows which intersect said first rows and which define angles of 15 with a plane normal to said axis of rotation.

6. An apparatus as defined in claim 2, said feed screw having a conically convoluted raised peripheral rib, and said first axis extending normal to said second axis.

7. A granulating apparatus as defined in claim 1, said casing being cylindrical and said extruder head being conical.

8. A granulating apparatus as defined in claim 7 said conical extruder head having an apex directly under the pressure screw.

9. A granulating apparatus as defined in claim 7 said conical extruder head rotating directly proximal to said outlet with the basis of the cone located directly under the pressure screw, and said wall portion projecting from the inner surface of the extruder head wall. 

1. A granulating apparatus comprising pressure-exerting conveying means including a casing having an outlet and a pressure screw rotating in said casing and operative for conveying material to be granulated towards said outlet under pressure; an extruder head rotating directly proximal to said outlet and being provided with a plurality of perforations, said perforations each being bounded in part by a wall portion projecting from a surface of the extruder head wall at one side of the respective perforations; and drive means for rotating said screw and said extruder head and for independently adjusting their respective speeds of rotation.
 2. A granulating apparatus as defined in claim 1, further comprising supply means for material to be granulated, including a hopper having an exit and a feed screw rotatable about a first axis in said hopper for conveying material through said exit, said casing communicating with said exit for receiving said material therefrom and said pressure-screw rotating in said casing about a second axis inclined to said first axis; and wherein said extruder head rotates about a third axis normal to said second axis and has a cylindrical peripheral wall provided with said perforations through which said material is extruded for granulation.
 3. An apparatus as defined in claim 2, said extruder head further comprising an internal support, and an internal and reinforcing structure connected with said cylindrical wall.
 4. An apparatus as defined in claim 2, wherein said perforations have diameters of between substantially one and 1.5 mm.
 5. An apparatus as defined in claim 2, wherein said wall comprises between two and six apertures in each square centimeter of surface area, the apertures being arranged in first rows which define with the axis of rotation of said head angles of 30* and in second rows which intersect said first rows and which define angles of 15* with a plane normal to said axis of rotation.
 6. An apparatus as defined in claim 2, said feed screw having a conically convoluted raised peripheral rib, and said first axis extending normal to said second axis.
 7. A granulating apparatus as defined in claim 1, said casing being cylindrical and said extruder head being conical.
 8. A granulating apparatus as defined in claim 7 said conical extruder head having an apex directly under the pressure screw.
 9. A granulating apparatus as defined in claim 7 said conical extruder head rotating directly proximal to said outlet with the basis of the cone located directly under the pressure screw, and said wall portion projecting from the inner surface of the extruder head wall. 